Methanocella conradii sp. nov., a thermophilic, obligate hydrogenotrophic methanogen, isolated from chinese rice field soil

Abstract

Background: Methanocellales contributes significantly to anthropogenic methane emissions that cause global warming, but few pure cultures for Methanocellales are available to permit subsequent laboratory studies (physiology, biochemistry, etc.). Methodology/Principal Findings: By combining anaerobic culture and molecular techniques, a novel thermophilic methanogen, strain HZ254T was isolated from a Chinese rice field soil located in Hangzhou, China. The phylogenetic analyses of both the 16S rRNA gene and mcrA gene (encoding the α subunit of methyl-coenzyme M reductase) confirmed its affiliation with Methanocellales, and Methanocella paludicola SANAET was the most closely related species. Cells were non-motile rods, albeit with a flagellum, 1.4-2.8 μm long and by 0.2-0.3 μm in width. They grew at 37-60°C (optimally at 55°C) and salinity of 0-5 g NaCl l-1 (optimally at 0-1 g NaCl l-1). The pH range for growth was 6.4-7.2 (optimum 6.8). Under the optimum growth condition, the doubling time was 6.5-7.8 h, which is the shortest ever observed in Methanocellales. Strain HZ254T utilized H2/CO2 but not formate for growth and methane production. The DNA G+C content of this organism was 52.7 mol%. The sequence identities of 16S rRNA gene and mcrA gene between strain HZ254T and SANAET were 95.0 and 87.5% respectively, and the genome based Average Nucleotide Identity value between them was 74.8%. These two strains differed in phenotypic features with regard to substrate utilization, possession of a flagellum, doubling time (under optimal conditions), NaCl and temperature ranges. Taking account of the phenotypic and phylogenetic characteristics, we propose strain HZ254T as a representative of a novel species, Methanocella conradii sp. nov. The type strain is HZ254T (= CGMCC 1.5162T = JCM 17849T = DSM 24694T). Conclusions/Significance: Strain HZ254T could potentially serve as an excellent laboratory model for studying Methanocellales due to its fast growth and consistent cultivability. © 2012 Lü, Lu.